godoc: periodically refresh package directory and search index.
godoc: periodically refresh package directory and search index.

R=adg, bradfitz
CC=golang-codereviews
https://golang.org/cl/55080043

nicot/tools,maddyonline/tools,jdhenke/tools,syreclabs/go-tools,magiccao/tools,dmitris/tools,sshetty10/tools,maddyonline/tools,cmars/tools,golang/tools,argandas/tools,josharian/tools,glasser/golang-tools,golang/tools,matryer/tools,josharian/tools,sshetty10/tools,cmars/tools,syreclabs/go-tools,sshetty10/tools,sshetty10/tools,syreclabs/go-tools,magiccao/tools,jdhenke/tools,josharian/tools,magiccao/tools,runcom/tools,4ad/tools,springning/tools,runcom/tools,glasser/golang-tools,matryer/tools,matryer/tools,cmars/tools,springning/tools,magiccao/tools,dmitris/tools,golang/tools,maddyonline/tools,matryer/tools,dmitris/tools,4ad/tools,argandas/tools,cw2018/tools,runcom/tools,springning/tools,nicot/tools,cw2018/tools,runcom/tools,argandas/tools,jdhenke/tools,josharian/tools,4ad/tools,argandas/tools,nicot/tools,golang/tools,jdhenke/tools,springning/tools,cw2018/tools,cmars/tools,cw2018/tools,glasser/golang-tools,syreclabs/go-tools,glasser/golang-tools,nicot/tools,syreclabs/go-tools,maddyonline/tools,golang/tools,syreclabs/go-tools,dmitris/tools